After Foo Fighters went on hiatus a couple of years ago, Dave Grohl didn't know what to do with himself. "I barbecued for fucking months, man," he says with a laugh. "I was doing eight briskets a week. It got a little dark."

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In actuality, he needed time to recuperate after spending nearly a year on the road on a mobile "throne," as he'd broken his leg falling off a stage mid-song at a 2015 gig in Sweden. "We had such a great run, but I couldn't walk yet," he says. "In order to take care of myself, I needed to get away from everything. I was in physical therapy for two or three hours a day for almost a year." So he told his bandmates he didn't want to touch an instrument for 365 days. "We've never taken that much time off," he says.

It didn't last. Six months "to the day" from when he announced his vacation, he wrote the charging hard rocker "Run," which became the first single from the band's upcoming ninth LP, Concrete and Gold, due September 15th. Now the band is back on the road, spending the summer in Europe and Asia before kicking off a North American leg of their tour in October with a star-studded festival, dubbed Cal Jam '17. The event will see the band playing alongside Queens of the Stone Age, Liam Gallagher, the Kills and more of the group's friends. "There's nothing more ridiculous than having a record-release party with 50,000 people instead of doing it at some bar down the street," Grohl says. "Let's just have it with a bunch of rowdy friends."

"I was in physical therapy for two or three hours a day for almost a year."

When Grohl began writing Concrete and Gold, though, he didn't have any friends around. "I don't think I was inspired at first," he says. "I just felt like I was creatively atrophied and had to start to exercise in order to wake the muscle up. After maybe 12 or 13 ideas, I send them to the guys and ask, 'Am I crazy? Or is this a record?' They say, 'Both.'"

To write the lyrics, Grohl rented an AirBnB in Ojai, California. "I brought a case of wine and sat there in my underwear with a microphone for about five days, just writing," he says. "It happened at the perfect time. I was inspired by what was going on with our country – politically, personally, as a father, an American and a musician. There was a lot to write about."

He hints at a bleak worldview on songs like "The Sky Is a Neighborhood," on which he narrates a sleepless night worrying about the state of the planet. On "T-shirt," he says, "I just wanna sing a long song/Pretend there's nothing wrong." And on the screeching "La Dee Da," he paid tribute to bands he liked when he was a teen – Psychic TV, White House and Death in June, the last of whom, known for fascist imagery, he admits is "controversial, which I didn't realize as a kid."

Once the tunes were in a decent place, Grohl was ready to record. "The last couple of albums had been made in ways that we were trying to get out of our comfort zone," he says, referring to 2014's Sonic Highways, which was recorded in different studios around the U.S., and 2011's Wasting Light, which they did in his garage. "I thought, 'What's the strangest thing for this band to do at this point?' And then I realized it was just to go into a studio and make a fucking album like a normal band."

The songs were catchy and melodic, but he knew they could be developed; so he reached out to a producer he'd befriended a few years back with a unique résumé. Although Grohl knew Greg Kurstin chiefly as a member of the indie-pop duo the Bird and the Bee, Kurstin is most famous as the producer and co-writer of Number One pop hits like Adele's "Hello," Pink's "Blow Me (One Last Kiss)" and Kelly Clarkson's "Stronger." "I was so in love with the Bird and the Bee because of their sense of melody, harmony, arrangement and composition," Grohl says. "It was clear that whoever was behind this music was not your everyday Guitar Center schmo." The duo connected and Grohl attempted to explain his vision.

"It was like he was describing a heavy-metal Sgt. Pepper odyssey," Kurstin says. "When I heard Dave's demos, they were going into all of these different areas that sounded new and exciting."

"I figured, OK, I can take care of the heavy part," Grohl says. "If he could do that Bird and the Bee thing over these massive riffs, then we will have made the album that I have always wanted to make, because of the love of Seventies AM gold radio and the love of a band like Motörhead."

Kurstin worked with the group on developing the tunes at Hollywood's EastWest Studios, writing lush arrangements for backing vocals and working with engineer Darrel Thorp place all the sounds in the mix.

"The band and Dave have such a drive so there's not a lot of motivating I needed to really do," producer Greg Kurstin says.Samon Rajabnik

As they worked, Grohl socialized with the other artists recording at EastWest, including Lady Gaga, Justin Timberlake and Shania Twain. He asked some people he met to sing on the record, but for the most part he won't say who. "Neither Adele nor Taylor Swift sang on the record," he says, clearing up rumors. But he did run into Boyz II Men's Shawn Stockman in the parking lot and asked him to craft some 30 backing vocal tracks to emulate a choir on the song "Concrete and Gold," blowing Grohl's mind. "When he left the room, I turned to everybody and said, 'The Boyz II Men dude just raised the fucking bar. Every song has to be that big.'" Other guests he is willing to reveal at press time include the Bird and the Bee's Inara George, saxophonist Dave Koz and the Kills' Alison Mosshart.

Kurstin says finding room for everything was easy, other than redoing a few drum takes, because working on the album was fun. "The band and Dave have such a drive so there's not a lot of motivating I needed to really do," he says. "The drive that Dave has, where he just has this excitement when he comes in the studio, is infectious."

Now that the record is done and the group is touring again, Grohl feels rejuvenated. He's looking forward to attempting another season of his HBO musicology and travel show Sonic Highways "sometime when I can," but mostly he's just enjoying being on the road and walking by himself. "I lent the throne to Axl Rose because he broke his foot awhile back, and I went to the show to see them," he says. "It was the first time I'd been in the audience, watching someone perform in this thing, and I thought, 'That is the most ridiculous fucking idea.'"